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11 Jan 1999

Volume 74, Issue 2, pp. 161-325

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Intrinsic optical confinement and lasing in InAs–AlGaAs submonolayer superlattices

N. N. Ledentsov, A. F. Tsatsul’nikov, A. Yu. Egorov, P. S. Kop’ev, A. R. Kovsh, M. V. Maximov, V. M. Ustinov, B. V. Volovik, A. E. Zhukov, Zh. I. Alferov, I. L. Krestnikov, D. Bimberg, and A. Hoffmann

Appl. Phys. Lett. 74, 161 (1999); http://dx.doi.org/10.1063/1.123281 (3 pages) | Cited 6 times

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We study the optical properties of structures composed of stacked InAs submonolayer insertions in an AlGaAs matrix grown on a GaAs(100) surface. The increased refractive index in the active region necessary for waveguiding is caused by the absorption peak due to excitons trapped by monolayer-height InAs islands. Despite a very low average InAs concentration, a thin AlGaAs buffer layer and an absorbing GaAs substrate photopumped lasing in the visible spectral range is already realized at low excitation density. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.45.+h Stimulated emission
78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Third-order optical nonlinearity of the carbon nanotubes

Xuchun Liu, Jinhai Si, Baohe Chang, Gang Xu, Qiguang Yang, Zhengwei Pan, Sishen Xie, Peixian Ye, Junhua Fan, and Meixiang Wan

Appl. Phys. Lett. 74, 164 (1999); http://dx.doi.org/10.1063/1.123282 (3 pages) | Cited 54 times

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Third-order optical nonlinearity of the carbon nanotubes was investigated with both 30-ps-wide and 8-ns-wide Nd:YAG laser beams. Both 1064 and 532 nm were used in each case. The nonlinear optical temporal response was obtained both on the picosecond scale and on the nanosecond scale, and the corresponding mechanism is discussed. Finally, we have compared the average contribution of one carbon atom to the third-order optical nonlinearity in the carbon nanotubes with that in C60, finding some enhancement of the third-order optical nonlinearity in the carbon nanotubes. © 1999 American Institute of Physics.  
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.An Optical susceptibility, hyperpolarizability
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.40.Ri Fullerenes and related materials

Pulse separation control for mode-locked far-infrared p-Ge lasers

A. V. Muravjov, R. C. Strijbos, C. J. Fredricksen, S. H. Withers, W. Trimble, S. G. Pavlov, V. N. Shastin, and R. E. Peale

Appl. Phys. Lett. 74, 167 (1999); http://dx.doi.org/10.1063/1.124221 (3 pages) | Cited 6 times

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Active mode locking of the far-infrared p-Ge laser giving a train of 200 ps pulses is achieved via gain modulation by applying an rf electric field together with an additional bias at one end of the crystal parallel to the Voigt-configured magnetic field. Harmonic mode locking yields a train of pulse pairs with variable time separation from zero to half the roundtrip period, where pulse separation is electrically controlled by the external bias to the rf field. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Three-dimensional optical circuitry using two-photon-assisted polymerization

Mukesh P. Joshi, Haridas E. Pudavar, J. Swiatkiewicz, P. N. Prasad, and B. A. Reianhardt

Appl. Phys. Lett. 74, 170 (1999); http://dx.doi.org/10.1063/1.123283 (3 pages) | Cited 50 times

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An approach using an as-formed solid bulk sample containing a blend of photocurable and thermally curable epoxies together with a highly efficient two-photon excitable fluorophore is demonstrated for in situ fabrication of three-dimensional optical circuitry with a precise control of dimension and spatial locations. Confocal volume images of a 1×2 splitter and a grating coupler are shown. End-fire coupling of a He–Ne laser beam into the 1×2 splitter has been achieved. © 1999 American Institute of Physics.
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82.35.-x Polymers: properties; reactions; polymerization
82.50.-m Photochemistry
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

High-temperature continuous-wave operation of λ∼8 μm quantum cascade lasers

S. Slivken, A. Matlis, C. Jelen, A. Rybaltowski, J. Diaz, and M. Razeghi

Appl. Phys. Lett. 74, 173 (1999); http://dx.doi.org/10.1063/1.123284 (3 pages) | Cited 10 times

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We report single-mode continuous-wave operation of a λ∼8 μm quantum cascade laser at 140 K. The threshold current density is 4.2 kA/cm2 at 300 K in pulsed mode and 2.5 kA/cm2 at 140 K in continuous wave for 2 mm long index-guided laser cavities of 20 μm width. Wide stripe (W ∼ 100 μm), index-guided lasers from the same wafer in pulsed operation demonstrate an average T0 of 210 K with other wafers demonstrating a T0 as high as 290 K for temperatures from 80 to 300 K. This improvement in high-temperature performance is a direct result of three factors: excellent material quality, a low-loss waveguide design, and a low-leakage index-guided laser geometry. © 1999 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.60.Pk Continuous operation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.66.Fd III-V semiconductors

Threshold reduction in pierced microdisk lasers

S. A. Backes, J. R. A. Cleaver, A. P. Heberle, J. J. Baumberg, and K. Köhler

Appl. Phys. Lett. 74, 176 (1999); http://dx.doi.org/10.1063/1.123285 (3 pages) | Cited 17 times

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GaAs microdisk lasers with holes pierced through the disk surface are investigated for their threshold characteristics. Disks are fabricated with either a single hole or two diametrically opposite holes at various distances from the disk outer edge. Even though the disk area is reduced by only 1%, we find that the lasing threshold for a disk with one hole is reduced by up to 50% compared to a disk with no hole. We attribute this reduction to the perturbation of nonlasing modes, which decreases the amplification of spontaneous emission in these modes and makes more carriers available to contribute to lasing. © 1999 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Experiments on the depolarization near-field scanning optical microscope

Ch. Adelmann, J. Hetzler, G. Scheiber, Th. Schimmel, M. Wegener, H. B. Weber, and H. v. Löhneysen

Appl. Phys. Lett. 74, 179 (1999); http://dx.doi.org/10.1063/1.122997 (3 pages) | Cited 13 times

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We demonstrate the operation of an apparatus which we call the depolarization near-field scanning optical microscope. It delivers subwavelength resolution with uncoated optical fiber tips without the need for additional modulation techniques. We show that—in the near field—the edges perpendicular to the incident optical polarization are imaged. This dependence on the orientation of the linear polarization as well as the influence of small ellipticities of the polarization state on the imaging process are measured on a well-defined test sample. The transition from near- to far-field imaging as a function of the tip height is demonstrated. The results are in good agreement with recent theoretical predictions. © 1999 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Visible and infrared rare-earth-activated electroluminescence from indium tin oxide Schottky diodes to GaN:Er on Si

M. Garter, J. Scofield, R. Birkhahn, and A. J. Steckl

Appl. Phys. Lett. 74, 182 (1999); http://dx.doi.org/10.1063/1.123286 (3 pages) | Cited 35 times

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Visible and infrared rare-earth-activated electroluminescence (EL) has been obtained from Schottky barrier diodes consisting of indium tin oxide (ITO) contacts on an Er-doped GaN layer grown on Si. The GaN was grown by molecular beam epitaxy on Si substrates using solid sources for Ga, Mg, and Er and a plasma source for N2. RF-sputtered ITO was used for both diode electrodes. The EL spectrum shows two peaks at 537 and 558 nm along with several peaks clustered around 1550 nm. These emission lines correspond to atomic Er transitions to the 4I15/2 ground level and have narrow linewidths. The optical power varies linearly with reverse bias current. The external quantum and power efficiencies of GaN:Er visible light-emitting diodes have been measured, with values of 0.026% and 0.001%, respectively. Significantly higher performance is expected from improvements in the growth process, device design, and packaging. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices

Intersubband absorption in boron-doped multiple Ge quantum dots

J. L. Liu, W. G. Wu, A. Balandin, G. L. Jin, and K. L. Wang

Appl. Phys. Lett. 74, 185 (1999); http://dx.doi.org/10.1063/1.123287 (3 pages) | Cited 50 times

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The intersubband absorption in self-assembled boron-doped multiple Ge quantum dots is observed. The structures used consist of 20 periods of boron-doped Ge dot layers and undoped Si barriers. The infrared absorption as a function of wavelength is measured by Fourier transform infrared spectroscopy using a waveguide geometry. Absorption peaks in the mid-infrared range have been observed, which are attributed to the transitions between the first two heavy hole states of the Ge quantum dots. The polarization dependence measurement is used to study the nature of the transitions. This observation suggests the possible use of multiple Ge quantum dots for infrared detector application. © 1999 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators
85.60.Gz Photodetectors (including infrared and CCD detectors)

Optimization of active regions in midinfrared lasers

J. T. Olesberg, Michael E. Flatté, B. J. Brown, C. H. Grein, T. C. Hasenberg, S. A. Anson, and Thomas F. Boggess

Appl. Phys. Lett. 74, 188 (1999); http://dx.doi.org/10.1063/1.123288 (3 pages) | Cited 9 times

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The ideal performance of bulk, quantum well, and superlattice active regions for III–V interband midinfrared lasers are compared according to the maximum net gain per unit current density. Based on this figure of merit, which is appropriate for high-power as well as near-threshold operation, InAsSb quantum well active regions should have an order of magnitude lower threshold current than bulk InAs at room temperature. Optimized four-layer superlattices based on the InAs/GaInSb material system, however, should have two to ten times lower threshold currents than the quantum well active regions. Optimal thicknesses for these active regions were evaluated assuming a separate confinement region design. For the four-layer superlattices the optimal thickness is substantially thinner than has been commonly grown: 3 periods rather than 40 periods. © 1999 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
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Raman studies on phonon modes in cubic AlGaN alloy

H. Harima, T. Inoue, S. Nakashima, H. Okumura, Y. Ishida, S. Yoshida, T. Koizumi, H. Grille, and F. Bechstedt

Appl. Phys. Lett. 74, 191 (1999); http://dx.doi.org/10.1063/1.123289 (3 pages) | Cited 39 times

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Cubic AlxGa1−xN alloy layers have been successfully grown for x = 0−1 by gas-source molecular beam epitaxy on cubic-SiC/Si substrates, and the compositional dependence of the transverse-optic (TO) and longitudinal-optic (LO) phonon modes has been studied by Raman scattering. The LO-mode frequency of mixed crystals shows a systematic variation from the pure cubic AlN phase to the cubic GaN phase (one-mode type). On the contrary, there are two branches for the TO mode varying slowly in frequency with the composition (two-mode type). This behavior is explained within a random-element-isodisplacement model including the effect of polarization field. Our result indicates a strong polarization field acting on the cation-nitrogen bonds. © 1999 American Institute of Physics.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors

Nanotube self-organization: Formation by step-flow growth

Oleg A. Louchev and Yoichiro Sato

Appl. Phys. Lett. 74, 194 (1999); http://dx.doi.org/10.1063/1.123290 (3 pages) | Cited 25 times

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The growth kinetics of carbon nanotubes is considered within the framework of a step-flow kinetics model proposed in 1951 by Burton, Cabrera, and Frank [W. K. Burton, N. Cabrera, and F. C. Frank, Philos. Trans. R. Soc. London, Ser. A 243, 299 (1951)] as a general mechanism for defectless crystal growth. The model reveals that the nucleation of the next layer and its consecutive growth can inhibit the growth of the underlying layers leading to the formation of observed nanotubular “bamboo” structures. © 1999 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.05.ub Fullerenes and related materials
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
64.60.Q- Nucleation
81.07.-b Nanoscale materials and structures: fabrication and characterization

Well-aligned carbon nitride nanotubes synthesized in anodic alumina by electron cyclotron resonance chemical vapor deposition

S. L. Sung, S. H. Tsai, C. H. Tseng, F. K. Chiang, X. W. Liu, and H. C. Shih

Appl. Phys. Lett. 74, 197 (1999); http://dx.doi.org/10.1063/1.123291 (3 pages) | Cited 70 times

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Vertically aligned carbon nitride nanotubes with a uniform diameter of about 250 nm have been synthesized on a porous alumina membrane template (50–80 μm thick) in a microwave excited plasma of C2H2 and N2 using an electron cyclotron resonance chemical vapor deposition system. A negative dc bias voltage was applied to the substrate holder of graphite to promote the flow of ionic fluxes through the nanochannels of the alumina template. This allowed the physical, and subsequent chemical, absorption of species on the walls of the nanochannels that resulted in the formation of the carbon nitride nanotubes. The hollow structure and vertically aligned properties of the nanotubes have been clearly verified by field-emission scanning electron microscope images. The absorption band between 1250 and 1750 cm−1 in the Fourier transform infrared spectroscopy spectrum proves that nitrogen atoms have been incorporated into an amorphous network of carbon. © 1999 American Institute of Physics.
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81.05.ub Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
78.30.Na Fullerenes and related materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Tr Fullerenes and related materials
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Hydrogen uptake in alumina thin films synthesized from an aluminum plasma stream in an oxygen ambient

Jochen M. Schneider, André Anders, Björgvin Hjörvarsson, Ivan Petrov, Karol Macák, Ulf Helmersson, and Jan-Eric Sundgren

Appl. Phys. Lett. 74, 200 (1999); http://dx.doi.org/10.1063/1.123292 (3 pages) | Cited 38 times

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We describe the hydrogen uptake during the synthesis of alumina films from H2O present in the high vacuum gas background. The hydrogen concentration in the films was determined by the 1H(15N,αγ)12C nuclear resonance reaction. Furthermore, we show the presence of hydrogen ions in the plasma stream by time-of-flight mass spectrometry. The hydrogen content increased in both the film and the plasma stream, as the oxygen partial pressure was increased. On the basis of these measurements and thermodynamic considerations, we suggest that an aluminum oxide hydroxide compound is formed, both on the cathode surface as well as in the film. The large scatter in the data reported in the literature for refractive index and chemical stability of alumina thin films can be explained on the basis of the suggested aluminum oxide hydroxide formation. © 1999 American Institute of Physics.
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68.55.Nq Composition and phase identification
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Bonding configurations of nitrogen absorption peak at 960 cm−1 in silicon oxynitride films

Haruhiko Ono, Taeko Ikarashi, Yoshinao Miura, Eiji Hasegawa, Koichi Ando, and Tomohisa Kitano

Appl. Phys. Lett. 74, 203 (1999); http://dx.doi.org/10.1063/1.123293 (3 pages) | Cited 21 times

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We investigated bonding configurations of nitrogen atoms in silicon oxynitride films, resulting in a 960 cm−1 absorption peak, which is a higher frequency than that for Si3N4 (840 cm−1). The 960 cm−1 peak was observed in the films for which an N 1s x-ray photoemission peak was observed with a binding energy of about 398.6 eV, which has been reported as a binding energy associated with the �Si–N–Si� structure. However, the 960 cm−1 peak was absent in the films for which the N 1s peak was observed at about 397.8 eV, being close to the binding energy associated with the Si3�N structure. We conclude that the absorption peak at 960 cm−1 arises from the �Si–N–Si� structure of doubly bonded N atoms with two Si atoms, not affected by any oxygen atoms. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.50.Lt Crystal binding; cohesive energy
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators

Electric-field-induced insulator–metal transitions in thin films of charge-ordered rare-earth manganates

V. Ponnambalam, Sachin Parashar, A. R. Raju, and C. N. R. Rao

Appl. Phys. Lett. 74, 206 (1999); http://dx.doi.org/10.1063/1.123294 (3 pages) | Cited 50 times

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Thin films of charge-ordered Nd0.5Ca0.5MnO3, Y0.5Ca0.5MnO3, and Nd0.5Sr0.5MnO3 have been prepared on Si(100) and LaAlO3(100) substrates by the nebulized spray pyrolysis of organometallic precursors. Small electric fields induce insulator–metal transitions in the films with the resistivity decreasing with increasing current. The current–voltage characteristics are non-ohmic and show some hysteresis. The current-induced negative differential resistance found in these manganate films could have potential technological applications. © 1999 American Institute of Physics.
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73.61.Ng Insulators
75.47.Gk Colossal magnetoresistance
72.60.+g Mixed conductivity and conductivity transitions
73.50.Fq High-field and nonlinear effects
75.70.Ak Magnetic properties of monolayers and thin films
71.30.+h Metal-insulator transitions and other electronic transitions
71.45.-d Collective effects

Two species model for deposition and erosion of carbon-nitrogen films

F. D. A. Aarão Reis and D. F. Franceschini

Appl. Phys. Lett. 74, 209 (1999); http://dx.doi.org/10.1063/1.123295 (3 pages) | Cited 9 times

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We propose a model of random deposition and erosion for carbon–nitrogen film growth. Particles C and N represent carbon and nitrogen atoms and are released with probabilities p and 1−p, respectively. Particle C aggregates upon contact with the surface. Particle N annihilates with a top C (N) with a probability of q (1). The line p = q/2 separates the regimes of growth and erosion. As p decreases for fixed q the deposition rate decreases, while the bulk concentration of N and the surface roughness increase. It describes qualitatively the growth of plasma deposited carbon–nitrogen films, and is in good quantitative agreement with results in acetylene–nitrogen atmospheres. © 1999 American Institute of Physics.
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81.15.Aa Theory and models of film growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.60.Bs Mechanical and acoustical properties
62.20.Qp Friction, tribology, and hardness

Femtosecond pump-probe investigation on relaxation of photoexcitations and spectral narrowing of photoluminescence for poly(para-phenylenevinylene)

Sae Chae Jeoung, Yong Hee Kim, Dongho Kim, Ja-Young Han, Min Sik Jang, Jung-Ik Lee, Hong-Ku Shim, Cheon Min Kim, and Choon Sup Yoon

Appl. Phys. Lett. 74, 212 (1999); http://dx.doi.org/10.1063/1.123296 (3 pages) | Cited 3 times

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Photoinduced absorption spectra and their temporal profiles of poly(para-phenylenevinylene) thin film exhibit a strong correlation with an appearance of spectrally narrowed emission bands. The dependence of transient absorption signals on excitation and probe power denotes much lower saturation intensity in photoinduced absorption than that in stimulated emission arising from the identical photoexcitations, singlet excitons. We interpreted the peculiar emission bands in terms of superradiance or superfluorescence with a time constant of around 1 ps rather than amplification of spontaneous emission from uncorrelated emitters. © 1999 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
78.47.-p Spectroscopy of solid state dynamics
78.55.Kz Solid organic materials

Photomelting of selenium at low temperature

Vladimir V. Poborchii, Alexander V. Kolobov, and Kazunobu Tanaka

Appl. Phys. Lett. 74, 215 (1999); http://dx.doi.org/10.1063/1.123297 (3 pages) | Cited 35 times

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We report on a photoinduced phenomenon in solids, namely, photomelting at low temperature. We have found that both trigonal and amorphous selenium can be molten by illumination with light at a temperature of ∼ 77 K. This phenomenon is pure optical (athermal) and it is associated with light-induced breaking of the interchain (intermolecular) bonds in selenium. The photomelting is important for basic science (as an example of photoinduced phase transition in condensed matter and as a key photoinduced phenomenon in selenium and related materials) and for applications (as a tool for fine manipulation with shape of solids by light at low temperatures). © 1999 American Institute of Physics.
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61.50.Lt Crystal binding; cohesive energy
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
79.20.Ds Laser-beam impact phenomena

Annealing effects and Te mixing in CdTe/CdS heterojunctions

Y. L. Soo, S. Huang, Y. H. Kao, and A. D. Compaan

Appl. Phys. Lett. 74, 218 (1999); http://dx.doi.org/10.1063/1.123298 (3 pages) | Cited 5 times

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Angular dependence of x-ray fluorescence techniques have been employed to investigate the effects of thermal annealing at various temperatures ranging from 340 to 387 °C on a series of CdTe/CdS heterojunctions. Changes in depth profiles of Te and Cd atoms in the CdS layer as a result of heat treatment has been observed. A simple model is proposed for comparison of the ratio of Te Kα to Cd Kα fluorescence yield at different annealing temperatures. Our results suggest that the concentration of migrated Te atoms in the CdS layer increases with the annealing temperature, and the Te/Cd ratio in the CdS layer could even become greater than that in CdTe with annealing temperatures higher than 370 °C. © 1999 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.Cc Kinetics of defect formation and annealing
78.66.Hf II-VI semiconductors

Silicon vacancy in SiC: A high-spin state defect

L. Torpo, R. M. Nieminen, K. E. Laasonen, and S. Pöykkö

Appl. Phys. Lett. 74, 221 (1999); http://dx.doi.org/10.1063/1.123299 (3 pages) | Cited 31 times

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We report results from spin-polarized ab initio local spin-density calculations for the silicon vacancy (VSi) in 3C– and 2H–SiC in all its possible charge states. The calculated electronic structure for SiC reveals the presence of a stable spin-aligned electron-state t2 near the midgap. The neutral and doubly negative charge states of VSi in 3C–SiC are stabilized in a high-spin configuration with S = 1 giving rise to a ground state, which is a many-electron orbital singlet 3T1. For the singly negative VSi, we find a high-spin ground-state 4A2 with S = 3/2. In the high-spin configuration, VSi preserves the Td symmetry. These results indicate that in neutral, singly, and doubly negative charge states a strong exchange coupling, which prefers parallel electron spins, overcomes the Jahn–Teller energy. In other charge states, the ground state of VSi has a low-spin configuration. © 1999 American Institute of Physics.
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71.55.Ht Other nonmetals
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
61.72.J- Point defects and defect clusters
71.70.Gm Exchange interactions

Mechanism of enhanced formation of C54–TiSi2 in high-temperature deposited Ti thin films on preamorphized (001)Si

S. M. Chang, H. Y. Huang, H. Y. Yang, and L. J. Chen

Appl. Phys. Lett. 74, 224 (1999); http://dx.doi.org/10.1063/1.123300 (3 pages) | Cited 17 times

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Enhanced formation of C54-TiSi2 in high-temperature deposited Ti thin films on preamorphized (001)Si has been investigated by high-resolution transmission electron microscopy in conjunction with autocorrelation function analysis. The increase in the thickness of the amorphous TiSix layer is due to the preamorphization implantation for the most part. The dominant effect of high-temperature sputtering is to increase the density of crystallites in the amorphous TiSix layer. The enhanced formation of C54–TiSi2 in high-temperature deposited samples is attributed to the more extensive presence of silicide crystallites, which serve as nucleation sites, in the amorphous TiSix layer than that in samples deposited at room temperature. © 1999 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
85.40.Ls Metallization, contacts, interconnects; device isolation
64.70.K- Solid-solid transitions
68.55.-a Thin film structure and morphology
61.72.uf Ge and Si
81.15.Cd Deposition by sputtering
61.72.Cc Kinetics of defect formation and annealing
73.61.At Metal and metallic alloys

Confirmation of proton beam bending in graded Si1−xGex/Si layers using ion channeling

D. G. de Kerckhove, M. B. H. Breese, P. J. M. Smulders, and D. N. Jamieson

Appl. Phys. Lett. 74, 227 (1999); http://dx.doi.org/10.1063/1.123034 (3 pages) | Cited 2 times

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A graded composition Si1−xGex/Si [001] layer, which has recently been proposed as a method for bending and extracting protons from high-energy particle accelerators, has been studied by angle-resolved ion channeling analysis using focused MeV proton and He+ beams. Backscattering spectrometry confirms that the composition is linearly graded and a maximum Ge concentration of 0.16 was measured at the epilayer surface. Off-normal planes {111} are curved with respect to the substrate by a total angle of 0.332° and efficient bending of channeled particles along the curved planes and into the substrate is confirmed. © 1999 American Institute of Physics.
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61.85.+p Channeling phenomena (blocking, energy loss, etc.)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
29.27.Ac Beam injection and extraction
29.27.Eg Beam handling; beam transport

Conducting barriers for vertical integration of ferroelectric capacitors on Si

S. Aggarwal, A. M. Dhote, H. Li, S. Ankem, and R. Ramesh

Appl. Phys. Lett. 74, 230 (1999); http://dx.doi.org/10.1063/1.123301 (3 pages) | Cited 11 times

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One of the issues impeding the commercialization of nonvolatile ferroelectric memories is the identification and development of a conducting diffusion barrier for the vertical integration of ferroelectric capacitors on Si-based transistors. We report results on the use of Ti–Al alloys as such a diffusion barrier. Our results indicate that it maintains its structural integrity and electrical conductivity after the deposition of a lead-based ferroelectric stack at 650 °C. The electrical properties of the capacitors were measured through the barrier layer by making direct contact to the diffusion barrier. The properties of the capacitors measured by direct contact to the Ti–Al alloy show clearly the absence of an insulating interfacial layer. Transmission electron microscopy and Rutherford backscattering studies confirm that there is no oxidation of the conducting barrier and no reaction between it and the electrode. © 1999 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors
85.40.Sz Deposition technology
73.61.At Metal and metallic alloys
81.15.Fg Pulsed laser ablation deposition
68.35.Fx Diffusion; interface formation
68.55.-a Thin film structure and morphology

Nanoscale reconstruction of surface crystallography from three-dimensional polarization distribution in ferroelectric barium–titanate ceramics

L. M. Eng, H.-J. Güntherodt, G. A. Schneider, U. Köpke, and J. Muñoz Saldaña

Appl. Phys. Lett. 74, 233 (1999); http://dx.doi.org/10.1063/1.123266 (3 pages) | Cited 94 times

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The three-dimensional orientation of polarization vectors at the surface of ferroelectric barium–titanate (BaTiO3) ceramics is evaluated using voltage-modulated scanning force microscopy (SFM). By applying an ac voltage to the conductive SFM tip, we measure the relative amount of the three orthogonal components Px, Py, and Pz, of the polarization vector at any surface point. The measured polarization orientation together with the actual domain-wall orientation allows a precise reconstruction of the crystallographic orientation of the investigated grains down to a 40 nm resolution. Excellent agreement is obtained when comparing this orientation with the crystallographic reconstruction revealed by etch patterns from the sample surface topography. We show that the surface topography manifests a domain structure, which was present in the past, while the actual ferroelectric domain configuration is revealed by the modulation technique. © 1999 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.35.B- Structure of clean surfaces (and surface reconstruction)
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
81.65.Cf Surface cleaning, etching, patterning
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
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